Answer
Firstly the v8 engine in the road cars are stock, or if from the performan
ce vehicle arms, it is slightly tuned. the race engine would be balanced, use the best components, and built for use for one race weekend.
the gearbox would be different to handle to difference in power between the engines. along with a racing clutch and lightened flywheel. these would not come in the road car.
i believe all the race cars run the ford 9-inch diff, although this may have changed. i do not beleive holden offers the ford 9-inch diff as standard, although this may have changed.
the tailshaft would also be stronger for the race cars then the road cars.
the race cars use something called a dry sump, not usually put in a road car, definitely not as standard equipment.
they are no unnecessary equipment attached to the motor of the race car, as in no air-conditioning, etc.
the battery is usually positioned in the boot.
whether you class this as mechanical, i do ont know, but the race cars do not use the standard wheel nuts to hold the wheel onto the car, and the race car has hydraulic/pneumatic jacks installed in the floor to lift it up at the pit stop.